30 H. HAYS BULLARD 



Bell ('11) states that the fat droplets of muscle fibers are all 

 isotropic. I have examined only a few specimens with the micro- 

 polariscope. The droplets were always singly and not doubly 

 refractive. This shows that the droplets are not a fat which is 

 fluid cr3''stalline in form, such as the cholesterine compounds. 



2. Solubility. The fat droplets of muscle fibers are readily 

 soluble in cold absolute alcohol and in ether. Ninety-five per 

 cent alcohol usually dissolves the droplets from frozen section or 

 teased preparations in a few minutes. Tissue fixed in seventy 

 per cent alcohol frequently shows a gradual diminution of the 

 quantity of fat. It is well recognized that tests of solubilit,y are 

 of little value in determining the chemical character of fats in 

 the tissues, especially as such fats, at least in most cases, are not 

 in a pure state but exist as mixtures. Neutral fat has usually 

 been considered insoluble in 70 per cent alcohol. However the 

 fat droplets of muscle fibers, having a diameter of but 1 to 3 m, 

 must be regraded as in an extremely fine state of division, thus 

 favoring prompt solution and, moreover, the quantit}' of solvent 

 is very many times that of the fat dissolved. The fact that fat 

 droplets in muscle fibers are sometimes dissolved by 70 per cent 

 alcohol does not prove that they are not neutral fat. 



3. Results with Scharlach R and Sudan III. Bell CIO) states 

 that I had shown clearly the great superiority of alkaline alco- 

 holic solutions of Scharlach R and mentions that my results had 

 not yet been published. My observations concerning the stain- 

 ing of fat droplets in muscle fibers with alkaline alcoholic solutions 

 of Scharlach R and Sudan in and with simple alcoholic solutions 

 of the same dyes, were made in the Laboratory of Anatomy of 

 the University of Missouri three years ago and are here given in a 

 corrected form. At that time I observed the position of fat drop- 

 lets in muscle fjJDers, a subject already discussed in this paper. 



Schlarlach R and Sudan in are usually employed as saturated 

 solutions in 70 to 80 per cent alcohol. Such solutions frequently 

 fail to stain the fat droplets of muscle fibers. The best results 

 arc obtained by heating the alcohol at the time of preparation 

 of the stains or by permitting a certain amount of evaporation 

 during the staining process. Even after an application of twenty- 



